Fibers utilized to produce woven and nonwoven textiles fall into the two broad categories: man-made and natural. Common man-made fibers include, for example, polyester, nylon, and polypropylene. Such thermoplastic polymers are melt spun into filaments which can be either air formed into nonwoven textiles directly as described in U.S. Pat. No. 2,689,199, which is incorporated herein in its entirety by reference, or cut into finite length fibers (known commonly as “staple fibers”) which can be formed into threads and yarn for woven or knit textiles. In addition, staple fibers can be formed directly into randomly oriented fiber webs and subsequently bonded together by a variety of means to form a nonwoven textile fabric. Such staple fibers generally are kinked when employed in nonwoven webs.
The most widely known natural fibers are cotton, wool, and silk. Wool and silk are exclusively used for woven textiles. Cotton is the dominant fiber for woven textiles although it also has minor utilization in nonwoven textiles. Cotton has limited use for modern nonwoven textile production due to its tendency to form fiber bundles when processed with the high speed carding typical of nonwoven production lines.
Wood pulp is one of the most common natural fibers and primarily is used for papermaking. Yet, wood pulp has a significant presence in the nonwoven textile industry when combined with man-made filament or staple fiber and the hydroentangling web bonding process. See, for example, U.S. Pat. Nos. 4,442,161 and 5,284,703, both of which are incorporated herein in their entirety by reference. Wood pulp has no direct presence in the woven textile industry. Rather, cellulose, the natural polymer that constitutes wood pulp fibers and other vegetative matter, is formed into a man-made class of filaments known as, for example, rayon (sometimes referred to as viscose), TENCEL®, lyocell, and derivatives thereof. Such man-made cellulosic fibers are used in both woven and nonwoven textiles. Such polymeric fibers are formed by chemically dissolving cellulosic matter, and spinning filaments from the cellulosic solution. For use in dry formed webs, man-made cellulosic fibers are typically crimped and cut into staple fibers. Fiber crimping is not required for wet formed webs.
Another major category of natural fibers is bast fibers. Bast fibers are found in the stalks of the flax, hemp, jute, ramie, nettle, Spanish broom, and kenaf plants, to name only a few. Typically, native state bast fibers are 1 to 4 meters in length. These long native state fibers are comprised of bundles of individual fibers which are straight and have a length between 20-100 mm. The bundled individual fibers are glued together by a class of plant resins called pectins.
Bast fibers have been used for at least 8,000 years for both woven textiles and cordage. However, such textiles and cordage were formed only with the native state bast fiber bundles. An example of a woven textile produced with flax bast fiber bundles is linen. More recently, as provided in U.S. Pat. No. 7,481,843, partially separated bast fiber is produced to form yarns and threads for woven textiles. However, yarns and threads are not suited for nonwoven fabrics.
Nonwoven web forming methods for natural and man-made staple fibers include wet forming. Wet forming is similar to the papermaking process, except that the ratio of forming water weight to fiber weight is much higher than that of conventional papermaking with wood pulp. The wet forming process accommodates staple fibers which are typically 6 mm-10 mm long and wood pulp fibers which are typically 2-4 mm long. However, a dry formed nonwoven web comprising individualized bast fibers is not presently available in the market.
Accordingly, there is a need for a nonwoven fabric which employs natural fibers having a length greater than 4 mm long and is not limited to wet forming. It is to solving this problem the present invention is directed.